Dozens of Republican convention delegates are hatching a new plan to block Donald Trump at this summer’s party meetings, in what has become the most organized effort so far to stop the businessman from becoming the GOP presidential nominee.

The moves come amid declining poll numbers for Trump and growing concern among Republicans that he is squandering his chance to defeat Democrat Hillary Clinton. Several controversies — including his racial attacks on a federal judge, his renewed call to temporarily ban Muslims from entering the United States and his support for changing the nation’s gun laws — have raised fears among Republicans that Trump is not really a conservative and is too reckless to run a successful race.

Given the strife, a growing group of anti-Trump delegates is convinced that enough like-minded Republicans will band together in the next month to change party rules and allow delegates to vote for whomever they want at the convention, regardless of who won state caucuses or primaries.

The new push is being run by people who can actually make changes to party rules, rather than by pundits and media figures who have been pining for a Trump alternative. Many of the delegates involved supported Sen. Ted Cruz (Tex.) in the primary race but say they are not taking cues from any of Trump’s vanquished opponents.

“This literally is an ‘Anybody but Trump’ movement,” said Kendal Unruh, a Republican delegate from Colorado who is leading the campaign. “Nobody has any idea who is going to step in and be the nominee, but we’re not worried about that. We’re just doing that job to make sure that he’s not the face of our party.”

The new wave of anti-Trump organizing comes as an increasing number of prominent Republicans have signaled that they will not support Trump for president.

In addition, House Speaker Paul D. Ryan (Wis.), who is slated to chair the Republican National Convention next month in Cleveland, said in remarks released Friday that House Republicans should follow their consciences on whether to support Trump.

Ryan has endorsed Trump. But his use of the word “conscience” could prove helpful to delegates organizing the anti-Trump campaign because they are seeking to pass a “conscience clause” that would unbind delegates and allow them to vote for anyone.

“I won almost 14 million votes, which is by far more votes than any candidate in the history of the Republican primaries,” he said. “I have tremendous support and get the biggest crowds by far and any such move would not only be totally illegal but also a rebuke of the millions of people who feel so strongly about what I am saying.”

People listen to the national anthem before Donald Trump speaks at a rally in Richmond on June 10. (Jabin Botsford/The Washington Post)

He added, “People that I defeated soundly in the primaries will do anything to get a second shot — but there is no mechanism for it to happen.”

Republican National Committee spokesman Sean Spicer responded in a statement, saying: “Donald Trump bested 16 highly qualified candidates and received more primary votes than any candidate in Republican Party history. All of the discussion about the RNC Rules Committee acting to undermine the presumptive nominee is silly. There is no organized effort, strategy or leader of this so-called movement. It is nothing more than a media creation and a series of tweets.”

Delegates involved in the effort disagree, but their plans face steep difficulties and would require rapid coordination among the thousands headed to Cleveland next month. Previous attempts to field a Trump opponent or to use convention rules to stop him have quickly fizzled, but the new fight revives the possibility of a contested convention.

The campaign kicked off in earnest Thursday night on a conference call with at least 30 delegates from 15 states, according to multiple participants. Unruh and Regina Thomson, another Colorado delegate, have recruited regional coordinators in Arizona, Iowa, Louisiana, Washington and other states.

Eric Minor, a GOP delegate from Washington state, said that he felt compelled to join Unruh’s group because “I hear a lot of people saying, ‘Why doesn’t somebody do something about this?’ Well you know what, I’m one of the people who can. There’s only 2,400 of us. I’m going to reach out to us and see if there seems to be momentum for this. And if there is, we’ll see where it goes.”

Steve Lonegan, a veteran GOP operative from New Jersey, is not a delegate but is advising the group and building financial support through a super PAC, Courageous Conservatives, that backed Cruz in the primary. The group has said it is willing to spend money on advertising and to help delegates across the country find one another.

Ever since Trump reached the threshold for claiming the GOP nomination last month, “I’ve woken up every day struggling to accept that he’s going to be our candidate,” Lonegan said. “He’s spent more time talking about getting Bernie Sanders voters to vote for him than conservatives. What do you think he has that Bernie Sanders’s supporters would like? A secret socialist agenda?”

Unruh, Minor, Lonegan and a number of others involved in the effort are former Cruz supporters, but they insist they are not working on his behalf. Cruz has said he would not accept the presidential nomination as a result of an attempt to strip Trump of the prize.

Other top Republicans, including Maryland Gov. Larry Hogan and Rep. Fred Upton (Mich.), said this week that they will not back Trump. Ohio Gov. John Kasich said he’s not ready to support Trump. And Richard Armitage, a deputy secretary of state in George W. Bush’s administration who is close with other members of the party’s national security establishment, announced that he plans to vote for Clinton if Trump is nominated.

Some of Trump’s top surrogates, including Sen. Jeff Sessions (R-Ala.) and Rep. Duncan D. Hunter (R-Calif.), have struggled to explain Trump’s policy positions and defend his statements and proposals in the wake of the mass shooting in Orlando.

“This isn’t going to go away,” warned Cecil Stinemetz, a delegate from Iowa participating in the new campaign. “Trump or others might say that these are just little groups who won’t do anything and it’ll fizz out — that’s not going to happen. Trump just continues to embarrass himself and his party, and this is not going to let up.”

Several factors will complicate any attempt to stop Trump.

First, Unruh’s plan to unbind the delegates will need support from a majority of the convention’s rules committee, which is scheduled to meet July 14 and 15 — just a few days before the convention formally convenes. If the proposal passes the committee, it would need to be ratified by a majority of convention delegates the following week.

Second, several delegates are deeply concerned about what they say are intimidation tactics by Trump, his campaign and some state party leaders.

One delegate, who commented on the condition of anonymity out of fear of retribution, wrote in an email that during his state party’s first convention organizing meeting, party leaders told the delegates that if they didn’t vote for Trump, “we would be removed from the floor and replaced with an alternate.”

Recruiting like-minded delegates may also be difficult, because the RNC has yet to release a list of the thousands of people elected to travel to Cleveland as delegates or alternates. A final list of names from each state and territory was due to the RNC on Monday, and party officials are reviewing the names to ensure that no elected delegate or alternate has a criminal record, according to party officials.

Privately, some RNC officials say they doubt that a full list will be released ahead of time.

RNC Chairman Reince Priebus and other top leaders have said delegates are required to reflect the results of state contests.

In response, a group of veteran Republican operatives is planning to raise up to $2.5 million to run an advertising campaign arguing that delegates can do whatever they want. The Citizens in Charge Foundation plans to bankroll the outreach campaign. It has paid for the publication of a book by Curly Haugland, a GOP delegate from North Dakota, who argues that delegates are already free to vote for anyone.

“It’s not an effort for a candidate or against a candidate, but it’s an effort to educate people on what their real authority is and have them get the comfort that they’re not alone,” said Eric O’Keefe, a party operative based in Detroit who is a member of the group. “There’s a whole network of like-minded people.”

“This is not a play for Cruz or Kasich or Ryan,” O’Keefe said. “I trust the delegates that if they understand their authority, they’ll nominate a good ticket.”